No description available.

No description available.

It appears impossible to nitrate cellulose in a medium of liquid sulfur dioxide either ~~th ruming nitric acid, a mixture of fuming nitric acid and sulfuric acid t a mixture of fuming nitric acid and phosphorus pentoxide, a mixture of fuming nitric acid, phosphorus pentox1de ana chlorine gas, or with nitrogen tetroxide. This is attributed to the fact that in each case the primary reaction ist hat of the formation of the compound N23209. / Ph. D.

Air pollution by sulfur dioxide is of great concern due to its harmful effects on environment, human beings, fauna and flora. Fossil-fuel-fired power plants are one of the major sources of SO2 emissions. Typically the concentration of SO2 in the flue gases of these plants is in the range of 2000 to 20000 ppm. Flue gas desulfurisation is one of the widely practiced strategies to control SO2 emissions. Aqueous phase oxidation of sulfur dioxide catalysed by carbonaceous particles is an attractive alternative to the conventional processes for flue gas desulfurisation because, amongst other reasons, sulfuric acid, the product of aqueous phase oxidation, finds extensive application in industry. In the literature it has been reported that sulfuric acid affects the solubility of sulfur dioxide and that activated carbon catalyses aqueous phase oxidation. However there is hardly any report on the systematic evaluation of the mechanism of the heterogeneous aqueous phase oxidation of sulfur dioxide which takes into account among other factors, the effect of sulfuric acid on the solubility of SO2 (particularly, at low levels of SO2 and sulfuric acid concentrations). Therefore the objective of the present work is to evaluate systematically the aqueous phase oxidation of SO2 in ppm levels with activated carbon as catalyst in a three-phase agitated slurry reactor and to model rigorously the solubility of SO2 in ppm levels in dilute sulfuric acid solutions and to estimate the concerned parameters experimentally. Strong effect of dilute concentrations of sulfuric acid on the solubility of SO2 is analyzed in terms of the influence of the acid on the equilibrium concentrations of the ionic species (HSO3¯ and SO4¯2 formed from the hydrolysis of SO2 (aq) and the dissociation of H2SO4 respectively) in SO2 - dil. H2SO4 systems. The analysis leads to a general expression relating the partial pressure of SO2 in the gas phase to the concentration of total dissolved SO2 and the concentration of sulfuric acid in the solution. Simple equations are obtained from the general expression for the cases of zero and high concentrations of sulfuric acid in the system, which in turn lead to direct experimental determination of the parameters, Henry's law constant and the equilibrium constant of hydrolysis of SO2 (aq). The developed model predicts the present experimental data as well as the data reported in the literature very closely. The dissolution of SO2, the hydrolysis of SO2 (aq) and the dissociation of H2SO4 are found to be instantaneous. From the dependency of the parameters on temperature, the heat of dissolution of SO2 is determined to be -31.47 kJ mol"1 and the heat of hydrolysis to be 15.69 kJ mol"1. The overall heat of solubility of sulfur dioxide is therefore -15.78 kJ mol"1. Preliminary reaction experiments have clearly indicated that SO2 (aq) does not react and HSO3¯ is the only reactant for aqueous phase oxidation of sulfur dioxide catalysed by activated carbon. The non-reactant SO2 (aq) deactivates the oxidation reaction by competing with HSO3¯ for adsorption on the active sites of the catalyst particles. However the catalyst particles become saturated with SO2 (aq) beyond a certain value of its concentration (saturation limit), which depends on temperature. A mechanism is proposed based on these observations to develop a rate model. The rate model also takes into account the effect of the concentration of the product sulfuric acid on the solubility of sulfur dioxide. The model predicts first order in HSO3¯ , half order in dissolved oxygen and a linear deactivation effect of 5O2(ag). The oxidation reaction is evaluated experimentally at various levels of the operating variables such as temperature and the concentrations of sulfur dioxide and oxygen in the inlet gas. In all experiments a pseudo steady-state region is observed where the gas phase concentration of SO2 reaches a steady value but the concentrations of HSO3¯ and total S (VI) in the liquid phase continue to change. Pseudo steady-state considerations lead to the determination of the initial estimates of the parameters of the rate model namely, the rate constant and the deactivation constant. These parameters are estimated from the transient profiles of the product (sulfuric acid) by solving the model equations by Runge-Kutta method along with Marquardt's non-linear parameter estimation algorithm. The predictions of the model with the estimated parameters match very well with the experimentally observed concentration profiles of S(VI) and HSO3 in the liquid phase and SO2 in the gas phase. The deactivation constant in the saturation range is independent of temperature and is 0.27, which indicates that the intrinsic rate constant is about four times greater than the observed rate constant. From Arrhenius equation-type dependency of the parameters on temperature, the activation energy for the oxidation reaction is determined to be 93.55 kJ mol"1 and for deactivation to be 21.4 kJ mol"1. The low value of activation energy for deactivation suggests a weak dependency of the deactivation on temperature, which perhaps is due to the weak nature of the chemisorption of SO2 (aq) on carbon.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Recent developments in the atmospheric treatment of low-grade nickel laterite ores at Anglo American plc has culminated in the conceptual iron-focused laterite (ARFe) process. In addition to the recovery of nickel and cobalt from laterite ore, this process uniquely aims to recover iron as a saleable by-product. The reduction of soluble iron(III) (Fe(III)) by sulfur dioxide gas (SO2) is central to the ARFe concept and represents a complex, multiphase system involving simultaneous gas-liquid mass transfer, thermodynamic speciation and chemical reaction. The chemistry of iron-containing systems is generally poorly understood and accurately predicting their behaviour is challenging, especially under aggressive hydrometallurgical conditions. The primary objective of this work is the development of an engineering model capable of describing the rate and extent of ferric reduction with SO2 under conditions typical of the ARFe process. Thermodynamic considerations provide a rigorous framework for the interpretation of chemical reactions, however little experimental data are openly available for the associated solution species in acidic iron sulfate systems. A key contribution of this work, and critical for the development of the overall model, is the direct measurement of speciation in iron sulfate solutions. Raman and UV-vis spectroscopy were utilised to make direct speciation measurements in the various subsystems of the Fe2(SO4)3-FeSO4-H2SO4-H2O system that were previously unavailable in the open literature. The FeSO+4 and Fe(SO4)– 2 species were explicitly identified and measurements were supported and rationalised by static computational quantum mechanical calculations and ultimately permit the calibration of a robust, ion-interaction solution model with the explicit recognition of the important solution species up to 1.6 mol/kg Fe2(SO4)3, 0.8 mol/kg H2SO4 over 25 – 90 C. Batch and continuous Fe(III) reduction kinetics were measured and the effects of initial Fe2(SO4)3 and H2SO4 concentrations, temperature and in-situ neutralisation quantified. The retardation effect of sulfuric acid was observed to be the most significant factor influencing the initial reaction rate and the achievable extent of reduction at fixed residence time, which varied between about 20 and 80 % after 180 minutes of reaction. A reaction mechanism that is limited by the slow ligand-to-metal electron transfer in the FeIIISO+3 solution species’ decomposition is proposed and spectroscopic measurements and computational quantum mechanical calculations are used to support this mechanism. A kinetic model, comprising a system of differential mass-balance equations, is incorporated into the thermodynamic framework. This reaction model permits the prediction of kinetic profiles over the full range of experimental conditions and can be incorporated into more elaborate simulation models of the ARFe circuit. The specific original contributions of this work are • The direct measurement of aqueous speciation in the Fe2(SO4)3-H2SO4-H2O system by Raman and UV-vis spectroscopy • The development of a modelling framework to characterise speciation, activity coefficients and solubility in the mixed Fe2(SO4)3-FeSO4-H2SO4-H2O system. • The measurement of Fe(III) reduction kinetics using SO2 in concentrated sulfate solutions as a function of initial composition and temperature. • The development of a solution reaction model of Fe(III) reduction with SO2 that accurately predicts the solution speciation and reaction rate with time as a function of composition and temperature. Lastly, the vast complexity of industrial systems will nearly always result in a lack of specific experimental data that are required for the development of phenomenological models. This work emphasises the crucial role that engineering studies hold in the generation of such data to derive maximum practical value for industrial process development and optimisation. / AFRIKAANSE OPSOMMING: Onlangse ontwikkelinge in die atmosferiese behandeling van lae-graad nikkel lateriet erts by Anglo American plc het gelei tot die konseptuele yster gefokus lateriet (ARFe) proses. Bykommend tot die herwinning van nikkel en kobalt uit laterite erts is hierdie proses uniek en daarop gemik om yster te herwin as ’n verkoopbare by-produk. Die vermindering van oplosbare yster(III) (Fe(III)) met swaeldioksied (SO2) is sentraal tot die ARFe konsep en verteenwoordig ’n komplekse, multifase stelsel wat gelyktydige gas-vloeistof massa-oordrag, termodinamiese spesiasie en chemiese reaksie behels. Die oplossingschemie van ysterstelsels word, oor die algemeen, swak verstaan en om hul gedrag akuraat te voorspel is ’n uitdaging, veral onder aggressiewe hidrometallurgiese kondisies. Die primêre doel van hierdie werk is die ontwikkeling van ’n ingenieursmodel wat die tempo en omvang van yster(III) vermindering met SO2 onder tipiese ARFe proses toestande beskryf. Termodinamiese oorwegings stel ’n streng raamwerk voor vir die interpretasie van chemiese reaksies, alhoewel daar egter min eksperimentele data openlik beskikbaar is vir die gepaardgaande oplossing spesies in suur yster(III) sulfaat stelsels. ’n Belangrike bydrae van hierdie werk, en van kritieke belang vir die ontwikkeling van die algehele model, is die direkte meting van spesiasie in yster(III) sulfaat oplossings. Raman en UV-vis spektroskopie is gebruik om direkte spesiasie metings te maak in die verskillende subsisteme van die Fe2(SO4)3-FeSO4-H2SO4-H2O stelsel wat voorheen nie in die oop literatuur beskikbaar was nie. Die FeSO+4 en Fe(SO4)– 2 spesies is ekplisiet geïdentifiseer, terwyl die metings ondersteun en gerasionaliseer is deur statiese kwantummeganiese berekeninge wat uiteindelik die kalibrasie van ’n robuuste, ioon-interaksie model tot gevolg hê wat ook die belangrike oplossingspesies duidelik beklemtoon tot en met 1.6 mol/kg Fe2(SO4)3, 0.8 mol/kg H2SO4 en tussen 25 – 90°C. Enkellading en kontinue yster(III) verminderingskinetika is gemeet en die gevolge van die aanvanklike Fe2(SO4)3 en H2SO4 konsentrasies, temperatuur en in-situ neutralisasie is gekwantifiseer. Die waargeneemde vertragingseffek van swaelsuur is die mees beduidende faktor wat die aanvanklike reaksietempo en die haalbare reaksie omvangsvermindering na ’n vaste residensietyd van 180 minute bepaal, wat wissel tussen ongeveer 20 en 80%. ’n Reaksiemeganisme word voorgestel wat beperk word deur die stadige ligand-totmetaal elektronoordrag in ontbinding van die Fe(III)SO+3 oplossing-spesies en wat verder deur spektroskopiese metings en kwantummeganiese berekenings ondersteun word. A kinetiese model, wat bestaan uit ’n stelsel van gedifferensieerde massa-balans vergelykings, is in die termodinamiese raamwerk geïnkorporeer. Hierdie reaksie-model laat die voorspelling van kinetiese profiele toe oor die volle omvang van die eksperimentele toestande en kan in meer uitgebreide simulasie modelle van die ARFe proces geinkorporeer word. Die spesifieke en oorspronklike bydraes van hierdie werk is • Die direkte meting van die spesiasie in die Fe2(SO4)3-H2SO4-H2O stelsel deur Raman en UV-vis spektroskopie • Die ontwikkeling van ’n modelraamwerk om spesiasie, aktiwiteitskoëffisiënte en oplosbaarheid in die gemengde Fe2(SO4)3-FeSO4-H2SO4-H2O stelsel te karakteriseer. • Die meting van yster(III) vermideringskinetieka deur SO2 in gekonsentreerde sulfate oplossings te gebruik as ’n funksie van die aanvanklike samestelling en temperatuur. • Die ontwikkeling van ’n oplossingsreaksie-model van yster(III) vermindering met SO2 wat die oplossing-spesiasie en reaksietempo met die tyd as ’n funksie van samestelling en temperatuur akkuraat voorspel. Laastens, die oorgrote kompleksiteit van industriële stelsels sal byna altyd lei tot ’n gebrek van spesifieke eksperimentele data wat nodig is vir die ontwikkeling van fenomenologiese modelle. Hierdie werk beklemtoon die belangrike rol wat ingenieursstudies speel in die generasie van data wat sodanig tot maksimum praktiese waarde vir industriële prosesontwikkeling en optimalisering lei.

Depth profiles of S(IV) and S(VI) in snow exposed to 20-140 ppbv SO₂ for 6 to 12 hours have been determined in 48 laboratory experiments. Surface deposition velocity (v(d)) averaged 0.06 cm s⁻¹. Well-metamorphosed snow, longer run times, higher SO₂ concentrations and colder snow were associated with lower values of v(d), and vice versa. Melting followed by draining increased v(d) greatly (0.14 cm s⁻¹. Any effect of ozone on SO₂ v(d) was undetectable. Most sulfur in the snow was as S(VI), even without added ozone, indicating the presence of other oxidants, especially in new snow. Four NO₂ deposition experiments (average v(d) = 0.007 cm s⁻¹), and one combined SO₂-NO₂ deposition experiment were conducted. Ozone, sunlight and SO₂ did not enhance NO₂ deposition; NO₂ and sunlight did not enhance SO₂ deposition. The deposition of SO₂ into a snowpack is modelled as an aqueous system, where the liquid water is considered to be present on snow grain surfaces. Gas transport into the snow, air-water partitioning, and aqueous-phase reactions are explicitly considered. Three oxidants (Fe- or Mn-catalyzed O₂, O₂, and H₂O₂) act to convert S(IV) to S(VI), acidify the film, and inhibit further S(IV) uptake. Model calculations illustrate the primary importance of liquid-water mass fraction (X(m)) and the secondary importance of oxidative reactions on SO₂ v(d) to snow. Model and experimental results are similar for assumed X(m) on the order of one percent. Experiments were also conducted on the incorporation of SO₂ into ice depositing from the vapor at -7 and -15°C. Remarkably, SO₂ is captured in deposited ice at concentrations comparable to Henry's Law equilibrium with water at 0°C. Ozone and HCHO appear to inhibit, not enhance, SO₂ capture. An aqueous-film model accounting for the capture of SO₂ by depositing ice was developed. S(IV) concentrations may be enhanced in the liquid-like layer on growing ice surfaces due to solute exclusion from the bulk ice and greatly-retarded diffusional transport from the ice/film interface, leading to significant incorporation into the ice despite low distribution coefficients. SO₂ snow scavenging ratios may be comparable to sulfate scavenging ratios in the remote troposphere.

No description available.

M.Sc. / [AuCl(PPh3)] was reacted with mixed thiols in the presence of silver(I) oxide, resulting in complexes of the type [Au(SC6H4X)(PPh3)] X= Cl, NH2,CH2, forming silver chloride as a by-product. In addition to the above series [Au(SCH2(C6H4)3(2-C6H5(C6H4N)] was prepared via a different route, where [AuCl3(2-C6H5(C6H4N)] was reacted with benzyl mercaptan under reflux in the presence of silver(I) oxide for 3 h, forming silver chloride as a by-product. Palladium complex [PdCl2(2-C6H5(C6H4N)] was prepared by reacting [PdCl2(MeCN)] with 2-phenylpyridine at room temperature for 2 h. All complexes were characterized by 1H, 13C, 31P{H} NMR, IR, mass spectrometry and elemental analysis. Characterization of the starting materials [AuCl3(2-C6H5(C6H4N)] and [PdCl2(2- C6H5(6H4N)] by single crystal X-ray diffraction confirmed their chemical formula. All complexes were reacted with sulfur dioxide (SO2) and the reactions were monitored by electrochemistry and UV-vis spectroscopy. The electrochemical study of the complexes, using cyclic voltammetry (CV) and Osteryoung square wave voltammetry (OSWV), showed one anodic peak, which is due to gold(I/III) and an unresolved peak due to thiolate ligand. Upon bubbling of SO2 to the complexes, there was an immediate change of colour from clear to yellow, the CV results showing an increase in current of the gold(I/III) peak. UV-vis spectroscopy studies showed a shift of peak form 250-286 nm, upon bubbling of SO2 to complexes.

The goal of this thesis is to investigate the kinetics and amount of SO2 uptake on hematite, which will act as a representative of mineral dust aerosol. The environmental reaction chamber used here will allow the variation of water vapor pressure to examine the effect of relative humidity (RH) on these parameters. The role of a common atmospheric oxidant, ozone, in the uptake process will also be investigated. The results will be presented with emphasis on the role of hematite in mineral dust aerosols as a sink of SO2, and the possible acidification of hematite particles through heterogeneous reaction pathways.

Sulfur dioxide is a primary pollutant and a known respiratory irritant. While there is a small level of background SO2, elevated concentrations are caused by industrial emissions. Muscatine, IA was designated as an area of nonattainment due to the persistent elevated levels of SO2 in the area. There are currently no available methods for predicting potential SO2 violations in Muscatine, and very little research was found investigating predictive modeling efforts. This thesis examines atmospheric conditions in Muscatine caused by SO2 emissions from facilities near the city. The main goals were to examine the plume dispersion model AERMOD for its ability to accurately map pollution levels, and to determine whether AERMOD could be used to predict SO2 concentrations when using meteorological forecast models as weather inputs. An historical analysis was performed using meteorological records from 2007 and AERMOD. The maximum emission limit was used in AERMOD. The resulting predicted concentrations were compared with concentrations reported at a monitoring site within the city. A forecasting analysis was also completed using two weather model forecasts (WRF and NAM) from March 2012 as meteorological input for AERMOD. Accurate daily SO2 emissions were obtained from each facility, and the corresponding rates were used in AERMOD. The resulting predicted concentrations were compared with monitored concentrations during the same time period. Overall, the historical analysis showed AERMOD's tendency to overestimate SO2 concentrations, particularly on days that also resulted in high monitored levels. The forecasting analysis resulted in favorable results with respect to the WRF weather forecast, but the NAM forecast created concentrations in AERMOD that were poorly correlated with monitored values. AERMOD still was likely to overestimate concentrations, but these overestimations were lessened due to more accurate emission information. Further research will be needed to further advance the prediction of pollution levels.